Aragonite is a polymorph of calcium carbonate that typically forms in distinct orthorhombic prismatic crystals or unique 'flos ferri' coralloid clusters. It is frequently found in limestone caves and hot spring deposits, where it precipitates from groundwater. Collectors should look for its characteristic star-shaped twinned crystals and its common yellow or white color palette.
Is this aragonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch aragonite with a known reference. Aragonite sits at Mohs 3.5-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Aragonite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Aragonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellow, blue, green, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, botryoidal, stalactitic.
Often confused with
Aragonite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside aragonite
Minerals reported to co-occur with aragonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCO₃
- Mohs hardness
- 3.5-4
- Density
- 2.93-2.95 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Botryoidal, Stalactitic
- Cleavage
- Distinct On {010}
- Fluorescence
- Often Fluorescent White, Yellow, Or Green Under SW UV
- Rarity
- Common
- Uses
- Collector, Ornamental, Scientific Research
- Host rock
- Sedimentary Environments, Hydrothermal Veins, And Hot Springs
- Typical price
- $5-50 for small specimens, $100-500 for large display clusters
Where rockhounds find aragonite
25 mapped spotsClassic worldwide localities
- Spain
- Mexico
- Morocco
- Czech Republic
- Namibia
U.S. states with aragonite
Each link opens a state-specific list of mapped rockhounding spots that produce aragonite.
Field-hunting tip
Look in sedimentary environments, hydrothermal veins, and hot springs country — that is the host setting where aragonite typically forms. If you start seeing calcite, dolomite, gypsum in float, you are in the right ground. Field specimens usually show a prismatic crystals, botryoidal, stalactitic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, Utah, Indiana — start trip planning there.
Common questions
How do you identify aragonite?+
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Find aragonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
